By Leah Wilson
Photos by Charles Garcia
In June 2018, engineers Charles Garcia and Cody Neyens examined several steel-lattice structures on the 230-kilovolt transmission line between the North Fork and Rifle substations. They were there to address potential issues that were previously noticed during line patrols; a few tower foundations were damaged due to soil movement and drainage problems. This caused the foundations to slide and the structures to twist.
“Work was scheduled to replace insulators and other line hardware, as well as replacing bent steel members and improving drainage around two structures, in the summer of 2019,” said Supervisory Electrical Engineer Jason Groendyk.
At the same time, fiscal year 2020 budgeting and planning were taking place for permanent repairs and possible structure replacements in the future.
Options and solutions
Several recommendations were made to address the immediate problems. These included replacing the bent legs, monitoring future movement and improving drainage around the structures.
Additionally, two long-term repair options were presented. The first option was to dig up the foundations one at a time and move them into the correct locations, then backfill and slope the soil for drainage away from the foundations. The second option was to replace the structure with a deep-foundation steel pole. After careful consideration, it was decided to go the first route.
“About 25 years ago when I was an apprentice, Montrose crews did this procedure before,” said Foreman II Lineman Craig Geesing. He explained that this fix had held up since, making it a viable option for future repairs instead of replacements.
“I was more involved in developing a future project to repair and replace these structures, and was informed [by HQ’s engineers] that the ‘temporary’ repair was actually going to hold up as a permanent repair,” Groendyk said.
Slip slidin’ away
There could be multiple reasons a foundation slides.
“Historically, it’s been an issue,” said Geesing. “There have been towers that have moved and changed in the past.”
“On mountains, some areas have weaker layers of soil. When saturated by water, areas can slip,” Garcia said. “It could be a tree clearing, road or drainage construction, a natural phenomenon or bad winters where there is more snow in the area than normal.”
Ultimately, there could be any number of causes spanning any amount of time.
“It depends on the situation,” said Garcia. “It could happen in a single storm or over the course of decades.”
There were many hands essential to the North Fork-to-Rifle restoration. Crews from Montrose, Shiprock, Craig and Cheyenne came together to participate in the project, as well as foremen, maintenance managers and civil engineers from Rocky Mountain and Headquarters.
The structure repair process is extensive.
“First you unhook the insulators from the conductors on the suspension structures and plumb them vertical,” Garcia said. “This balances out the loading and makes the loads vertical to the structure. You do this to each of the three insulators that are attached to the conductors, and the optical ground wires if needed.”
Geesing explained that after the replumbing, the crews monitor how the ground wires are moving. A crane is then attached to the tower leg to remove all load from the tower to the foundation. The load is calculated each time per structure. Then, once the tower is secure, a backhoe is used to dig down and around to the base of the foundation.
“The foundation will then be moved to the correct location to remove all bending and stresses in the members,” Garcia said. “I had to be there to address anything that came up since I design these structures.”
Once the foundation is in the correct position and the tower is straight, a backhoe is used to begin filling in and around the foundation. Finally, the crane can release the load from the tower.
With a project this extensive, a few unexpected obstacles were encountered. It wasn’t for lack of planning, however; often the extent of the work doesn’t fully reveal itself ahead of time. Garcia explained that sometimes they won’t even know what they’re up against until they start to move a structure.
For instance, during this project, a lot of rock was encountered, making it difficult to balance towers out and drill through and repair some of the structures. Another issue was difficulty driving to the towers. Many times, the crews had to improve the access roads by taking out trees and building safer turns for the large trucks that were necessary for the repairs.
In addition, water posed a threat to moving foundations; one tower was holding water due to an incorrectly installed drain.
Through perseverance, crews were able to complete a few of the tower repairs and save customers money in the process, as replacing structures with steel poles rather than repairing the existing structures would have been costly.
“It would be about $500,000 per structure,” Garcia noted. “Also, a steel pole replacement would take about six months to fabricate and deliver. A contract would have to be bid and a construction contractor selected to install the pole and foundation. This would include widening and making the access roads better for a large crane to set the pole and drill the large deep foundation.”
“Ground patrol is once a year and flown twice a year to monitor what they’ve done and what the status is,” Geesing explained. “It’s an ongoing process, but it saved them quite a bit of money as opposed to replacing or moving them.”
Overall, WAPA’s maintenance crews avoided $2.25 million in cost with this repair work.
Not done yet
“We dug up and moved the footers on two of them, the worst ones,” said Geesing. “We plumbed the insulators and put the links in the statics on quite a few. Fourteen more were identified as having bent steel. This August we will work on some more to get them straight and replace any bent steel.”
“There were structures that required foundation adjustments,” Garcia added. “We did three structures and the other two will be completed this summer. The schedule was dictated by the crew’s availability to do the work.”
The structures will continue to be observed for movement. Monitoring and repairing potentially damaged towers will be a yearly task for the next five to eight years.
Note: Wilson is an administrative analyst who works under the Wyandotte Services contract.
Crews, maintenance managers and engineers came together to address foundation issues in a project that was three years in the making.
This 15-degree base adaptor was one way crews were able to address the problem.
Shifting foundations can result in many issues for towers, such as the bowing visible in this photo.
Insulators being out of plumb were some of the issues crews needed to address. According to Garcia, “It doesn’t take much to change the tensions in the wires and put loads in the tower.”
Last modified on December 4th, 2023